Multiphase non-metallic compositions of matter



MULTIYHASE NON-METALLIC COMPOSITIONS 0F MATTER Fild June 28, 1968 Aptil7, 1970 w, s o ET AL 8 Sheets-Sheet 1' 1 As-Cast Transverse Section ofLiF-NaF (200K) FIG.

2 Unidirectionally Solidified Transverse Section of LiF-NaF (200K) FIG.

A ril 7, 1970 w. R. LASKO ET AL 3,50

MULTIPHASE NON-METALLIC COMPOSITIONS OF MATTER 8 Sheets-Sheet 3 FiledJune 28, 1968 inal Section 0 FIG.

Unidirectionally solidified Longitud LiF-NaF (200x) FIG. 4 As-CastTransverse Section of NaF-PbF (200K) MULTIPHASE NON-METALLICCOMPOSITIONS OF MATTER Filed June 28, 1968 AprilY, 1970 w, s o ET AL 8Sheets-Sheet 5 5 Unidirectiona FIG.

11y Solidified Transverse Section of NaF-Pblf (200x) FIG.

Unidirectionally solidified Longitudinal Se ction of NaF-PbF (200x)Aprilvl, 197-0 w. R. LASKO ET AL 3,505,218

MULTIPHASE NON-METALLIC COMPOSITIONS OF MATTER 8 Sheets-Sheet 4.

Filed June 28, 1968 FIG. 7 As-Cast Transverse Section of CaF' -LiF-NaF(200K) 8 Unidirectionally Solidified Transverse Section of CaF -LiF-NaFFIG.

April7, 19 10 LASKQ ET AL 3,505,218

MULTIPHASE NON-METALLIC COMPOSITIONS 0F MATTER 8 Sheets-Sheet 5 FiledJune 28, 1968 Unidirectinnally solidified Bongitudinal Section of CaF-LiF-NaF (200x) FIG.

April 7, 1970 w, s o ET AL 3,505,218

MULTIPHASE NON-METALLIC COMPOSITIONS OF MATTER Filed June 28, 1968 8Sheets-Sheet 6 25 553 2 3:22 3 If f* 3 J I g 2' LL POLISHING PLANE xPLANE B 7 7 if PLANE A -PLANE 0 April 7, 1970 w. R. LASKO ET AL3,505,218

MULTIPHASE NON-METALLIC COMPOSITIONS OF MATTER 8 Sheets-Sheet Filed June28, 1968 M07255 1 I I 5 m2; zaozx Z o? zoEmom wofimmtfi oom A 00MEDEEQEE 2555 10mm 08 08 00 -08, Ko a e 08.. .v

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'O POTENTIOMETER p n, 1970 w. R. LASKO ET A 3,505,218

MULTIPHASE NON-METALLIC COMPOSITIONS OF MATTER Filed June 28, 1968 8Sheets-Sheet 8 FIG."I4b

United States Patent 3,505,218 MULTIPHASE NON-METALLIC COMPOSITIONS OFMATTER William R. Lasko, 79 Granite Road, Glastonbury, Conn. 06033, andMonte C. Nichols, 1733 E. Silver, Tucson, Ariz. 87716Continuation-impart of application Ser. No. 637,004, May 8, 1967. Thisapplication June 28, 1968, Ser. No. 747,416

Int. Cl. C09k 3/00; G02b 1/00; B01i 17/00 U.S. Cl. 252-1 16 ClaimsABSTRACT OF THE DISCLOSURE A solid, polyphase composition of mattercomprising a eutectic mixture of inorganic compounds is provided, thecomposition of the mixture being such that the cornponents thereof arereciprocally soluble in the liquid state, but freeze simultaneously at aconstant temperature into at least two different solid phases uponcooling from the liquid state, the composition having a microstructureof eutectic composition containing at least two solid phases, at leastone of said phases being in the form of an aligned, three-dimensionalcrystallites which are substantially parallel to a common direction.Additional compositions of eutectic mixtures comprising an inorganiccompound and a member selected from the group consisting of Water, anelement and mixtures thereof are also provided. Such compositions,depending on the orientation relationships between the phases, areuseful as components in either optical or electromagnetic devices.

Furthermore, an improved method of forming a solid, polyphasecomposition of matter comprising a eutectic mixture of theabove-identified components is provided in which the improvement residesin employing said components.

CROSS-REFERENCES TO RELATED APPLICATIONS This application is acontinuation-in-part of U.S. application Ser. No. 637,004, filed May 8,1967, and now abandoned which in turn is a continuation of U.S.application Ser. No. 350,510, filed May 9, 1964, now abandoned.

BACKGROUND OF THE INVENTION Generally stated, the subject matter of thepresent invention relates to new and useful polyphase eutectic mixturesof inorganic compounds in which the phases have a fixed crystallographicrelationship to one another, and to methods for producing such polyphasesystems.

Objects of the present invention are new polyphase eutectic mixtures ofmetal salts, metal oxides, or combinations of metal salts and metaloxides having microstructures in which one or more of the phases ispresent in the form of very thin three-dimensional lamellae orcrystallites which are parallel or substantially parallel to a givendirection.

A further object of the present invention is a method of producing suchpolyphase eutectic mixtures of inorganic compounds.

Additional objects and advantages of the invention will be set forth inpart in the description which follows, and in part will be obvious fromthe description, or may be realized by practice of the invention, theobjects and advantages being realized and attained by means of themethods, processes, instrumentalities and combinat ons particularlypointed out in the appended claims.

ice

THE INVENTION To achieve the foregoing objects and in accordance withits purpose as embodied and broadly described, the present inventionrelates to a solid, polyphase composition of matter comprising aeutectic mixture of inorganic compounds, in which the cation moiety ofsaid compounds is a metal selected from the group consisting of Group1A, 13, 2A, 2B, 3A, 3B, 4A, 4B, 5A, 6A, 6B and 8 metals of the PeriodicTable of Elements, and the anion moiety of said compounds is a memberselected from the group consisting of oxides, halides, sulfides,carbonates, chromates, nitrates, nitrites, sulfites, silicates, phosphates, zirconates, zirconites, titanates, tungstates, sulfates, andlanthanates; the composition of the mixture being such that thecomponents thereof are reciprocally soluble in the liquid state, butfreeze simultaneously at a constant temperature into at least twodilferent solid phases upon cooling from the liquid state, thecomposition having a microstructure of eutectic composition containingat least two solid phases, at least one of said phases being in the formof an aligned, three-dimensional crystallites which are substantiallyparallel to a common direction.

The present invention further provides a method of forming the solid,polyphase composition of matter hereinabove described which comprisesthe steps of establishing a eutectic mixture, heating the mixture to atemperature above the eutectic temperature to melt a portion thereofthroughout its entire cross-sectional area and to establish aliquid-solid interface, undirectionally solidifying at the liquid-solidinterface by mov ng the interface in a direction such as to give thedesired lamellae orientation, subjecting the interface to a coolingmedium while the interface is moving in said direction to therebysimultaneously solidify at the interface at least two separate eutecticphases, and causing atleast one of the eutectic phases to grow in theform of three-dimensional crystallites which are normal to theliquid-solid interface and parallel to the growth direction by regulatng the solidification rate and the thermal gradient of the liquid at theliquid-solid interface so that the ratio of the thermal gradient in theliquid phase at the solid-liquid interface to the solidification rate isbetween about 0.1 and 1000 C/cm. /hr., the improvement wherein theeutectic mixture comprises inorganic compounds, as hereinabovedescribed.

The invention consists of the novel methods, processes, steps andimprovements shown and described.

According to one embodiment of the present invention, polyphase eutecticmixtures of inorganic compounds have been produced havingmicrostructures which consist predominantly of very fine,three-dimensional phase lamellae or crystallites which may becharacterized as plates or rods, of one phase imbedded in another phase,said lamellae or crystallites being substantially parallel to a commondirection.

Such polyphase products are produced by establishing a liquid-solidinterface in a multiphase eutectic mixture of inorganic compounds, andcausing the interface to be moved in a unidirectional fashion whilesimultaneously cooling the interface through an appropriatetransformation temperature. In this way, three-dimensional crystallitesof each phase of the eutectic grow or form normal or approximatelynormal to the interface or solidification front between the transformedand untransformed eutectic mixture and parallel to the growth directionover great distances, e.g., up to 1 or 2 inches, or 1 or 2 feet, or even1 or 2 meters, or even longer. Further, the parallel microstructureextends throughout substantial volumes of the uni-directionallysolidified product.

When the lamellae formed are three-dimensional plates or platelets,these may be substantially parallel to one another, as well as parallelor substantially parallel to the growth direction throughout the entirevolume of the specimen.

The three-dimensionl plate-like lamellae, however, need not be andfrequently are not parallel to one another throughout the entire volumeof the composition.

Thus, for example, the plates or platelets in one volumetric section ofthe composition may form an angle with the plates or platelets in anadjoining volumetric section of the composition. The plates or plateletsfrom section to section of the composition are, however, parallel to acommon direction, even through, from section to section, the plates orplatelets may not be substantially parallel to each other. Thisphenomenon will be desrcibed more fully hereinbelow in connection withthe drawings.

When the lamellae formed are rods, these are substantially parallel toeach other over the entire specimen, as well as substantially parallelto a common direction.

Regardless of whether rod-like or plate-like lamellae are formed, thelamellae in the microstructure of the products described herein extendin a direction which is normal to or substantially normal to thesolidification front.

In the solid compositions of this invention, the microstructures arecomprised of a eutectic mixture of inorganic compounds. The inorganicmixtures are such that the inorganic components thereof are reciprocallysoluble in the liquid state. Upon cooling, the mixtures from the liquidstate, however, two (or more) different types of inorganic crystals(hereinafter sometimes called phases) freeze simultaneously at a fixedtemperature, called the eutectic temperature. Examples of eutecticmixtures which may be used to form the products of the present inventionare cited for illustrative purposes in Table I.

pounds of the type described are within the purview of this invention,wherein the chemical element is a member selected from the groupconsisting of Group 1A, 1B, 2A, 23, 3A, 3B, 4A, 4B, 5A, 5B, 6A, 6B, and8 elements of the Periodic Table of Elements. As employed in the instantspecification and claims the Periodic Table of Elements shall be definedto be according to Mendeleef as set forth in the Hadnbook of Chemistryand Physics,

46 Edit, 1965-1966, published by The Chemical Rubber Co., which table isincorporated by reference as part of the present specification.

The eutectic compositions suitable for use herein are preferably thoseselected from that class of inorganic eutectic mixtures which can becontrolled by appropriate, preferably solidification techniques, to givea microstructure which consists of fine three-dimensional crystallites,e.g., plates or rods, of one of the phases imbedded in another or secondphase, sometimes referred to as the matrix.

With such eutectics, the crystallites (e.g., plates or rods) togetherwith the matrix are referred to as the groundmass and the groundmass isof eutectic composition.

With other eutectics suitable for use herein, if one of the phases isforced to grow as parallel plate-like crystallites, the other phase maygrow in the same manner. In products made from such eutectics, theparallel phase lamellae may be referred to as the groundmass of thecompositions. Here again, the groundmass of such products is of eutecticcomposition.

Eutectic mixtures of inorganic salts and/or oxides having the abovedescribed characteristics, i.e., the ability of at least one of theeutectic phases to solidify in the form of three-dimensional plate-likeor rod-like crystallites, are referred to in the art as normaleutectics, and

Metal fluoride salts and metal oxides. CaF -CaO, PbF -PbO.

Combination systems .II LiCl-LizCOs, NaBr-NmO-SOa, PbBl'z-Pbo,

Kcrmcrot Ba0-B,o3-sio,, C'aO-BzO SiOg, Sl'O-BgOySiOg.

It should be understood that the eutectic systems given are suitable forthe preparation of the new and useful in the table are intended to bemerely illustrative and not limiting.

It will be noted from the table that the compositions include eutecticmixtures of inorganic compounds, e.g.,

class of materials of the present invention.

In Table II, typical normal eutectics comprising inorganic metal saltsare classified in accordance with their as cast structure.

TABLE IL-AS CAST STRUCTURE OF NON-METALLIC EUTECTICS inorganic metalsalt, inorganic metal oxide, or a mixture of salts and oxides. Among themetal salts may be mentioned the halides, sulfides, carbonates,'chromates, nitrates, nitrites, sulfites, silicates, phosphates,zirconites, titanates, tungstates, sulfates, lanthanates, and the like.

Eutectic mixtures comprising water as a component, as well as elements,in combination with inorganic com- The mixtures used as a startingmaterial to make the new and useful products of the present inventionmay be of true eutectic composition, or may deviate from true eutecticcomposition. In either event, the parallel lamellate groundmass will beof eutectic composition.

When the starting admixture deviates from true eutectic composition, theproducts will still have a parallel lamellar groundmass ormicrostructure of eutectic composition. However, in this embodiment,relatively large-non-eutectic crystals of one of the compounds aredistributed throughout the parallel lamellar eutectic groundmass ormicrostructure. These relatively large noneutectic crystals will bereferred to hereinafter as proeutectic crystals.

Mixtures deviating from true eutectic composition may be considered tocomprise a eutectic portion, i.e., a portion which undergoes a eutecticreaction as this term is defined hereinabove, and a proeutectic portion,i.e., a portion which does not undergo a eutectic reaction. When such amixture is used as starting material, the resulting product willcomprise a parallel lamellar eutectic groundmass or microstructurehaving distributed therein relatively large proeutectic crystals. Thedistribution of the proeutectic crystals throughout the parallellamellae eutectic groundmass may be random or uniform.

For best results, the starting admixture used to form the product ofthis invention should be eutectic or substantially eutectic incomposition.

The invention will be described with reference to the accompanyingdrawings, in which:

FIGURE 1 is a photomicrograph (200x) of transverse section of an as castmicrospecimen of the LiFNaF eutectic of Table II;

FIGURES 2 and 3 are photomicrographs (200x) of transverse andlongitudinal sections, respectively, of the same LiF-NaF eutectic, butunidirectionally solidified in accordance with this invention;

FIGURE 4 is a photomicrograph (200x) of a transverse section of an ascast microspecimen of the NaF--PbF eutectic of Table II;

FIGURES 5 and 6 are photomicrographs (200x) of transverse andlongitudinal sections, respectively, of the same NaF-PbF eutectic, butunidirectionally solidified in accordance with this invention;

FIGURE 7 is a photomicrograph (200x) of a transverse section of an ascast microspecimen of the ternary eutectic CaF LiF-NaF;

FIGURES 8 and 9 are photomicrographs (200 of transverse and longitudinalsections, respectively, of the same CaF LiFNaF eutectic, butunidirectionally solidified in accordance with this invention;

FIGURE 10 is a schematic sketch illustrating dependence of lamellarappearance upon the plane of sectioning of a specimen exhibitingplate-like lamellae;

FIGURE 11 is a sketch showing measurements which may be taken todetermine the lamellar orientation of a specimen exhibiting plate-likelamellae;

FIGURE 12 is a stereographic projection of lamellar normals of varioussections of a microspecimen of the type shown in FIGURES 2 and 3. Growthdirection on this projection is vertical, and the plane of projection isa longitudinal section;

FIGURE 13 is a schematic diagram of an apparatus which may be used inmaking the structures of the present invention;

FIGURES 14(a) and 14(1)) are schematic diagrams of specimens undergoingunidirectional solidification; and

FIGURE 15 is a typical plot of temperature versus time for a specimenundergoing unidirectional solidification.

As is apparent from FIGURES 2, 3, 5, 6, 8 and 9, the microstructures ofthe polyphase systems of the present invention comprise thin lamellae orcrystallites of one eutectic phase which are specifically oriented withrespect to thin lamellae or crystallites of other eutectic phases.

FIGURES 1-3 are photomicrographs of the NaF-LiF eutectic.

Transverse and longitudinal sections of the same NaF-LiF microspecimenunidirectionally solified in accordance with this invention are shown inFIGURES 2 and 3, respectively.

As shown in FIGURES 2 and 3, the thin lamellae of each phase arethree-dimensional plate-like in appearance, and within volumetricsections, all of the lamellae of one phase of the NaF--LiF eutectic areparallel or substantially parallel to one another and therefore alsoparallel or substantially parallel to the lamellae of the other phase.

The as cast LiFNaF eutectic is shown in FIGURE 1 for comparison withFIGURES 2 and 3. Note in FIG- URE 1 that the phases are randomlyoriented with respect to each other.

FIGURES 4, 5 and 6 are photomicrographs of the NaF-PbF eutecticidentified in Table II. Transverse and longitudinal sections of aspecimen unidirectionally formed in accordance with this invention areshown in FIGURES 5 and 6. As shown by FIGURES 5 and 6, the lamellae ofeach eutectic phase are three-dimensional, rod-like crystallites, whichare parallel to each other. The as cast NaF--PbF eutectic is shown inFIGURE 4 for comparison purposes. Note in FIGURE 4 that the orientationof the phases of the as cast structure is random with respect to eachother.

FIGURES 7, 8 and 9, are photomicrographs of the ternary eutectic CaF--LiF-NaF. The unidirectionally solidified specimen shown in FIGURES 8and 9' reveals parallel NaF rods in a LiF and CaF matrix. As shown byFIGURE 7, the orientation of the phases of the as cast material is quiterandom.

FIGURES 10 is a schematic illustration of the microstructure achieved bythis invention and is intended to bring out the three-dimensional natureof the lamellae of the unidirectionally solidified polyphase eutecticmixtures of the inorganic compounds.

It will be noticed in FIGURE 10 that the appearance of a series ofparallel plates depends very strongly upon the particular polishingplane taken through the specimen. If the plane of the microspecimen isnot quite parallel to the growth direction as in planes C and D of FIG-URE 10, and/or depending upon how the lamellae happened to grow in aparticular section relative to the plane of the microspecimen, all sortsof lamellar structures will be observed. The true orientation of theplates in any section can onl be obtained by measuring the angles atwhich the plates intersect two intersecting planes, as is brought out inFIGURE 11. The angle between the planes, 5, and the angle A between agiven arbitrary direction in one of the planes and the intersection ofthe two measuring planes must also be known. From these measurements thedirection of the plane normals can be determined most easily by means ofa stereographic projection. If the lamellae grow into the liquid, thelamellae normals should all lie on the equator of a stereographicprojection, the plane of which is a longitudinal section and the axis ofwhich is the growth direction. The results of a stereographic analysisof the sections of the specimen shown in FIGURES 2 and 3, for instance,as well as other sections, confirm, within the limits of experimentalerror, the fact that the lamellae do grow into the liquid parallel tothe growth direction in spite of the rather odd way they sometimesappear in particular microspecimens.

In any event it has been established that when the microstructure of aunidirectionally solidified inorganic eutectic mixture displaysplate-like lamellae, e.g., the NaFLiF eutectics of FIGURES 2-3, theselamellae are parallel or substantially parallel to each other withinsections of the specimen, and the lamallae from section to section ofthe specimen are parallel or substantially parallel to the growthdirection.

When the microstructure of a unidirectionally solidified eutecticmixture of inorganic compounds comprises rodlike lamellae of one phaseimbedded in another or second phase, e.g., the NaF-MgF eutectic ofFIGURES 5-6, these rod-like lamellae will be parallel or substantiallyparallel to each other throughout the specimen, and also parallel to thegrowth direction.

The unique microstructure of the unidirectionally solidified inorganiceutectic mixtures of the present invention lead to unique physicalproperties.

The properties of the controlled composite crystals may be isotropic oranisotropic depending on the orientation relationships between the twophases and the nature of each phase. Inorganic eutectic mixtures with anordered phase are frequently transparent and therefore useful ascomponents in either optical or electromagnetic devices. In optics,certain of the unidirectionally solidified inorganic eutectic mixturesfind utility as diffraction grantings, prisms, and high temperaturelenses. Because of their unique microstructural regularity, otherproperties (viz. heat conductivity, ductility, adsorption, etc.) of theinorganic eutectic mixtures can also be put to good use. For example,the instant procedures and compositions can be used to produce astructural ceramic as well as to fabricate substrates for micromodulesto insure good heat conductivity.

The microstructures of the unidirectionally solidified eutectic mixturesmay be characterized in terms of the parallelism of the lamellae, i.e.,plates or rods, making up the microstructure, and also in terms of thesize and shape of the lamellae.

In terms of physical dimensions, when the lamellae are three-dimensionalplate-like crystallites, these are extremely thin and have a thicknessof about 0.02 to about 20 microns, and usually between about 0.04 andmicrons. The width of the plate is at least three times the thicknessand is generally greater than ten times the thickness. The length of thelamellae is generally greater than the width, and may vary from about 50microns to l or 2 inches or more.

As has been noted hereinabove, these plate-like lamellae are arrangedwithin the specimen so as to be substantially parallel to one anotherover appreciable distances within a section; and between sections, theplate like lamellae are substantially parallel to the common growthdirection, which, as has been pointed out, is frequently parallel to thesolidification direction, but which may be artificially inclined at anangle, depending upon the application.

When the lamallae are rods, these have a diameter of about 0.02 tomicrons, usually between about 0.02 to 10 microns, and a length which isgreater than the diameter, generally greater than microns, and usuallybetween about 100 microns and 1 to 2 inches. These crystallites in theform of rods are substantially parallel to each other and to the commongrowth direction throughout the entire specimen.

The parallelism of the phase of the inorganic eutectic mixtures may bedescribed by stereographic projection, which is a technique used todescribe angles and direction in three dimensions on a two-dimensionalsheet of paper. The theory of stereographic projection is described inmany standard works on geometry and trigonometry.

Briefly, in stereographic projection, planes, axes and angles areconveniently represented on a sphere. The crystal or origin of allplanes, axes and angles is assumed to be very small compared with thesphere (known variously as the reference sphere or polar sphere) and tobe located exactly at the center of the sphere. Planes of the crystal,or in the present instance, the lamellae in the microstructure of theinorganic eutectic, can be represented by extending the lamallae untilthey intersect the sphere in a great circle. The normals to plate-likelamellae can alternately be used. The microspecimen is assumed to be sosmall that all lamellae pass through the center of the sphere. If allplanes of the crystal, or in this instance, if all of the lamellae ofeach phase are projected upon the sphere in this manner, it will befound that the axes of the rod-like lamellae or normals to theplate-like lamellae bear the same reaction to each other as do thelamellae within the microstructure of the eutectic and so exhibit,without distortion, the angular relation of the lamellae within themicrostructure.

The parallelism of the lamellae in the microstructure may be designatedby a concept called spherical excess, using the method of stereographicprojection.

If the lamallae within the microstructure are perfectly parallel, all ofthe projections of these lamellae (axes for rods, normals for plates)will intersect the sphere at two diametrically opposite points. Thestereographic projections of lamallae having this relationship areassigned a spherical excess of 0 percent.

If the arrangement of the lamellae is completely random, the projectionswill occur in diametrically opposite pairs all over the surface of thespheres. The stereographic projections of such lamellae are said to havea spherical excess of percent.

If, however, the lamellae within the microstructure are not completelyparallel, but nearly so, the projections of the lamellae (axes for rods,normals for plates) will intersect the surface of the sphere over asmall angular range. Because the projection lines always intersect thesphere at two diametrically opposite points, two diametrically oppositeand equal small angular ranges will occur but it is only necessary toconsider one of them. The projections of the lamellae in themicrostructure, accordingly, are said to have a spherical excess, whichis expressed by the percentage of the surface of the hemisphere boundedby the curves connecting the points on the surface of the sphere whichextend from the described projections of the lamellate of themicrostructure.

The theory of stereographic projection and the concept of sphericalexcess may be applied to determine the arrangement of the lamellae inthe microstructures of the products of the present invention.

When the microstructure of the unidirectionally solidified mixtures ofinorganic compounds comprise rods, or rod-like crystallites, the rodsare parallel or substantially parallel to each other and to a givendirection, e.g., the growth direction, over the entire specimen.

For inorganic eutectic mixtures having rod-like microstructures, thespherical excess of the stereographic projection of the rods varieswithin the range of from about 0 to 20 percent, rarely over 10 percent,and usually from 0 to 5 percent.

Stereographic projection has also been used to measure the orientationof the lamellae of the unidirectionally solidified eutectics of thepresent invention having microstructures comprising plate-like lamellae.

Within sections of the specimen (see FIGURES 2-3), the spherical excessof the stereographic projection of lamellae has been found to be fromabout 0 to 20 percent, rarely over 10 percent, and usually from about 0to 5 percent.

When plate-like microstructures exist, the term section or volumetricsection refers to a volume of the specimen in which the plate-likelamellae are parallel or substantially parallel to the lamellae of theother phase of, for example, a two phase system.

For inorganic microstructures comprising plate-like lamellae, theorientation of the plate-like lamellae from section to section isdetermined by stereographic projection of the lamellae normals, withrespect to the growth direction. When the growth direction on theprojection is vertical, and using a longitudinal section of themicrospecimen, the stereographic projections of the platelike lamellanormals deviate from the equator by less than 30, rarely over 20", andusually under 5. This means that the plate-like lamellae deviate frombeing parallel to the growth direction by the indicated degrees.

FIGURE 1, as brought out above, is a photomicrograph of a transversesection of the LiFNaF eutectic as cast. The same eutectic was used inmaking the specimen shown in FIGURES 2-3. Comparing FIGURE 1 withFIGURES 23, it is obvious that the microstructures' are radicallydifferent. Thus, in FIGURE 1, crystal growth started at many points andgrew outward in all directions within the liquid, and a random, overallstructure was produced. The orientation of the lamellae as is shown inFIGURE 1 varies from area to area. In terms of spherical excess, thestereographic projections of the lamellae in the specimen whosemicrostructure is shown in FIGURE 1 would have a spherical excessapproaching 100 percent, i.e., completely random. For comparison thestereographic projections of the lamellae in FIGURES 2-3 would have aspherical excess, within volumetric sections, of less than 5 percent. Asimilar analysis applies to FIGURES 4-6 and FIGURES 7-9, respectively.

The method of unidirectionally solidifying eutectic mixtures ofinorganic compounds will be described in connection with FIGURES 13,14(a), 14(b) and 15.

As shown in FIGURE 13, a typical apparatus comprises a hollow, tubularinduction furnace 2 having heating coils 4 suitably attached to a powersource, now shown. Slideably mounted within the induction furnace is acrucible 6, which holds the eutectic mixture 8. Projecting upwardlythrough the bottom of the crucible and into the specimen is athermocouple 10.

The induction furnace may, if desired, be equipped with a closure member12 which is fitted with a tube 14, through which may be admitted aninert bleed gas, such as argon, krypton, neon and so forth.

Crucible 6 is fitted with a suitable drive mechanism (not shown) to pullthe crucible through the furnace. The drive mechanism is readilyadjustable to change the rate at which the crucible is drawn through theinduction furnace.

Spaced below the induction furnace and surrounding the crucible iscooler 22 through which a suitable cooling fluid is passed and projectedor sprayed upon the surface of the crucible as it passes therethrough.

The following examples describe methods of unidirectionally solidifyingeutectic mixtures of inorganic compounds. Though illustrative, it shouldbe understood that the invention is not limited to the specific methodor apparatus described, but is broad enough to encompass all methods andapparatus which will be obvious to those skilled in the art from thedescription herein.

Example I.-Preparation of a binary eutectic composition of NaF and LiFThis example demonstrates the preparation of a primary eutecticcomposition comprising NaF and The system used is a eutectic compositioncomprising 40 percent NaF and 60 percent LiF (mole percent). The as castsolid was prepared by heating an intimate mixture of the two materialsin a platinum crucible at 700 C. in a Temco furnace and raising thetemperature to 800 C., removing the contents, and cooling in air.

The structure of the resulting solidified eutectic mixture beforecontrolled solidification is shown in FIGURE 1. The individual phasescan be readily distinguished when the specimen has been suitablypolished and etched. It can also be observed from the micrograph, FIGURE1, that the orientation of the two phases is quite random with respectone to the other, although some preferred orientation exists over smallareas. The system, as is, thus acts as an aggregation of randomlyoriented crystallites or colonies.

The as cast material was then placed in a graphite boat in a frictiondrive trolley furnace with a nichrome heating element. The sample wasmelted initially in sections and then with the furnace moving at about 3cm./hr. with argon flow and at a temperature of 800 C. Three passes ofthe heat zone were made across the specimen. Photomicrographs of themicrostructure of the controlled sample are shown in FIGURES 2-3. Asshown in FIGURES 2-3, the two phases of the unidirectionally solidifiedmicrostructure present a fixed relationship to one another. In additionto having a fixed crystallographic orientation, the phases occur asalternating lamellae on the order of a few microns in thickness.

Example II.Preparation of a binary eutectic composition of PbF and NaFThis example demonstrates the preparation of a binary eutecticcomposition of PbF and NaF.

The system used is a eutectic of 68 percent PbF and 32 percent NaF (molepercent). The as cast material was prepared as described in Example 1.The Temco furnace temperature, in this case, however, was maintained at650 C. for 1 hour. The structure of the as cast material is shown inFIGURE 4. Normal colony structure with NaF rods is indicated.

Using the procedure of Example 1, this eutectic system wasunidirectionally solidified under argon in a graphite boat at about 1cm./hr. and at a maximum temperature of about 780 C. The controlledstructure, as shown in FIGURES 5-6, consists of NaF rods in a P bFmatrix. The NaF rods appear reasonably well aligned.

Example III-Preparation of :a ternary eutectic composition of CaF NaFand LiF This example demonstrates the preparation of a ternary eutecticcomposition of CaF NaF and LiF.

The ternary system (CaF NaFLiF) illustrates the applicability of theinvention to the more complex threecomponent eutectic systems. Thissystem has a eutectic at 10 percent CaF 36.5 percent NaF and 53.5percent LiF (mole percent).

The as cast melt was prepared by heating at 1800" C. and cooling in air.The microstructure, as cast, shown in FIGURE 7, reveals NaF rods in aLiF and CaF matrix. The as cast material was placed in a graphite boatand melted in the zone melter described in Example 1. The material waszone passed twice at about 4-5 cm./hr. to mix the components. Thematerial was then controlled at 2.7 crn./hr. at about 850 C. Transverseand longitudinal sections of the controlled structure are shown inFIGURES 8-9, respectively.

In carrying out the examples, the apparatus of FIG- URE 13 may readilybe used. For instance, the induction furnace 2 may consist of an outertube, e.g., Vycor, fitted at its bottom with an RF induction load coil.A curcible, e.g., graphite, drilled to hold the specimen, may beslideably mounted in the outer tube. The crucible may then be drawnthrough the furnace in the direction of the arrow shown in FIGURE 13 bya suitable drive mechanism (not shown).

After charging the apparatus with the specimen, power to the inductioncoil is turned on, and water fed to the quenching fixture. An inert gas,e.g., argon, can then be fed to the tube, as shown in the drawing, tominimize the oxidation of the melt. The heat input of the inductioncoils and the temperature and rate of water flow to the quenchingfixture or water cooler should be regulated to produce a solid-liquidinterface in the specimen Which extends across the entirecross-sectional area of the specimen in a direction substantiallytransverse to the direction of motion of the graphite crucible.

The drive mechanism for the crucible may then be turned on, and thecrucible drawn through the Vycor tube at the predetermined rate.

Temperature gradients in the liquid and the location of the liquid-solidinterface may be determined by recording and plotting the temperature ofa thermocouple bead as a function of the distance that the crucible hastravelled.

The temperature of the liquid and the thermal gradient at the interfaceare controlled by appropriately adjusting the power input to theinduction coil, the quantity of water used, and the rate ofunidirectional movement of the crucible.

FIGURE 14 is a schematic diagram of a typical specimen being subjectedto unidirectional solidification. As is shown in FIGURE 14, thesolid-liquid interface 24 extends across the cross-sectional area of thespecimen, and in a direction transverse to the unidirectional movementof the specimen in this example.

The thermal gradient, G, in the liquid at the liquidsolid interface, wasdetermined by recording and plotting the temperature of a thermocouplebead as a function of the distance that the movable part of theapparatus had travelled. A typical curve of this type is shown in FIG-URE 15. The temperature gradient, in the liquid, immediately in front ofthe interface, as determined by the slope of the curve, is in C./cm.

The rate of solidification, R, is determined from the number ofcentimeters of solidified alloy formed, and the time' required forformation. The solidification rate is expressed as cm./hr.

In preparing the controlled non-metallic eutectics of thepresent'invention having substantially parallel lamellae, it isimportant to control the thermal gradient (G) in the liquid at theinterface and the solidification rate (R) during the unidirectionalsolidification.

The thermal gradient in the liquid is defined as the change intemperature in the liquid per centimeter of length in the liquid phaseimmediately in front of the advancing interface. As the liquid eutecticis cooled, it will beappreciated that the temperature will change fromthat of the eutectic at its melting point, or above, i.e., when the meltis superheated, to that of the solidified eutectic. The thermal gradientis measured in accordance with the method described hereinabove.

'As is shown in FIGURE 14(a), the specimen as it is being subjected tounidirectional solidification, contains a solid-liquid interface 24, thespecimen below the interface being solid, as indicated at S, and abovethe interface being liquid, as indicated at L. As the specimen is pulleddownwardly through an apparatus of the type shown in FIGURE 13, theinterface will gradually move towards the top of the specimen. Atcommencement of operation, of course, the liquid phase can extend to thebottom of the specimen. The lamellae of the phases, as indicatedschematically at 25 and 26 of FIGURE 14(a) grow normal to the interface24, and also parallel to the direction indicated by the arrow in FIGURE14(a), this direction in this instance corresponding to thesolidification direction.

It is not, however, necessary that unidirectional forming commence atthe bottom of the specimen, nor need it be carried out over the wholelength of the specimen. Nor is it necessary that the entire specimen beliquid above the interface. It is simply necessary that a solid-liquidinterface be established, and that the solidification be controlled atsaid interface.

Although the direction of solidification has been described to bevertical, it should be understood that the solidification may be carriedout in any direction desired. Thus, for example, the solidificationdirection may be horizontal, or may form any angle with the vertical.Practical considerations may warrant the unidirectional solidificationbeing carried out over only a portion of the specimen. In this event,those portions of the specimen not subjected to unidirectionalsolidification may be cut away from the portion that has undergoneunidirectional solidification, if desired.

In any event, it will be apparent that the temperature of the liquidphase will vary with distance. This variation is called the thermalgradient, and is measured in C./ cm. So far as the present invention isconcerned, it is the thermal gradient in the liquid at the liquid-solidinterface, e.g., 24 in FIGURE 14(a) that is important.

Interface 24 in FIGURE 14(a) is referred to as the crystallizationfront, and it is at this interface that the plate-like or rod-likelamellae form. The crystallization front may be transverse to the net oroverall solidification direction, as shown in FIGURE 14(a), or it mayform other angles with the solidification direction. Usually, however,the crystallization front will be transverse to the solidificationdirection.

In FIGURE 14(b), for example, the interface 24 is shown to form an anglewith the net or overall solidification direction. The lamellae 25 and26, however, grow normal to the interface 24. In FIGURE 14(b), ofcourse, the lamellae'25' and 26 do not grow parallel to thesolidification direction, which is indicated by the arrow. Rather, theselamellae are parallel to a direction which is normal to thesolidification front 24'.

It will also be apparent that the liquid phase will solidify at a ratedepending upon the temperature of the liquid, the rate of cooling, andthe velocity of the specimen through the heating and cooling zones. Thesolidification rate,.R, is measured in cm./hr.

The solidification rate and thermal gradient in the liquid at theliquid-solid interface undergoing solidification, i.e., thecrystallization front, which are necessary to produce the lamellarmicrostructures described hereinabove, vary, depending upon the eutecticcompositions being unidirectionally solidified. In general, it may besaid that the solidification rate and the thermal gradient must be keptwithin a certain range, which range varies for each system whosemicrostructure is being controlled. The necessary solidification rateand thermal gradient will also depend to a certain extent on theimpurities in the system.

The ratio of the thermal gradient, G, at the crystallization front tothe solidification rate, R, is a good measure to assure formation of theparallel lamellae at the solid-liquid interface. In general, the ratioG/R may vary from about 0.1 to 1000, and is preferably between about 1to 300 C./cm, /hr. The optimum value, of course, depends to a largeextent upon the physical and chemical composition of the system beingsubjected to unidirectional solidification.

Although the method of forming unidirectionally solidified eutecticmixtures of inorganic compounds has been described in connection Withcylindrical specimens, it should be understood that the shape of thespecimen is not critical, and that the method is equally applicable tospecimens having various shapes, such as cubes, polygons, torroids andthe like. Care must be taken in unidirectionally solidifying suchspecimens, however, to insure that the liquid-solid interface undergoingsolidification is maintained perpendicular to the desired lamellaeorientation.

What is claimed is:

1. As a new article of manufacture, an anisotropic polyphase solidcharacterized by a microstructure of eutectic composition which is amember selected from the group of inorganic compound containingeutectics consisting of: KCL-LiCl; BaFe O BaFe O MgCl -KC1; Al 0 -TiOPbOWO PbOPbM O FeO- FeS; CoO--FeS; Li CO CaCO Li CO Na CO NaF-CaFNaF-LiF; NaFMgF NaF-PbF NaFCaF LiF; CdBI'g; CdBr -ZnBr NaIHgI KlHgIAgINaI; Ca(NO KNO Ca(NO NaNO K2804; Na O-P O C3.0P205 La O ZrON34P207N32W04 BaOZrO LiF; LiBr-LiF; CaF LiFNaF; CaF CaO; PbF PbO; LiClLiCO NaBrNa OSO PbBr PbO; KCl-I CrO BaOB O --SiO CaOB O SiO CaO-B O -SiOand SrO B O SiO the components of said eutectic composition beingreciprocally soluble in the liquid state; said eutectic compositionbeing further characterized by the ability to simultaneously form atleast two different solid phases at a constant temperature upon coolingfrom the liquid state;

said micro-structure of eutectic composition containing at least twosolid phases, at least one of the phases being in the form of aligned,three-dimensional crystallites which are substantially parallel to acommon direction over an extended distance.

2. The solid, polyphase composition of matter according to claim 1,wherein aligned crystallites have a rod-like form.

3. The solid, polyphase composition of matter according to claim 2,wherein the rod-like crystallites are substantially parallel to eachother and to a common direction, and have a spherical excess of lessthan 20 percent.

4. The solid, polyphase composition of matter of claim 2, wherein therod-like crystallites have a diameter of about 0.02 to 20 microns, and alength considerably greater than the diameter.

5. The solid, polyphase composition of matter of claim 2 wherein therod-like crystallites have a diameter of about 0.02 to microns, and alength of at least 100 microns.

6. The solid, polyphase composition of matter of claim 2, wherein therod-like crystallites are substantially parallel to each other, and havea spherical excess of less than 5 percent.

7. The solid, polyphase composition of matter according to claim 1,wherein the aligned, three-dimensional crystallites have a plate-likeform.

8. The solid, polyphase composition of matter according to claim 7characterized by a microstructure wherein three-dimensional plate-likecrystallites of one phase of the eutectic alternate withthree-dimensional, plate-like crystallites of another phase of theeutectic, the crystallites of both phases being substantially parallelto a common direction.

9. The solid, polyphase composition of matter of claim 7 wherein theplate-like crystallites are parallel to one another within volumetricsections of the microstructure, and parallel to a common direction fromsection to section.

10. The solid, polyphase composition of matter according to claim 9,wherein the stereographic projection of the plate-like crystalliteswithin a section have a spherical excess of less than percent, andwherein the plate-like crystallites of all sections are parallel to thecommon direction within 11. The solid, polyphase composition of matteraccording to claim 9, wherein the stereographic projection of theplate-like crystallites within a section have a spherical excess of lessthan 5 percent, and wherein the plate-like crystallites of all sectionsare parallel to the common direction within 5.

12. The solid, polyphase composition of matter of claim 7, wherein theplate-like crystallites have a thickness of about 0.02 to 20 microns, awidth of at least three times the thickness, and a length considerablygreater than the width.

13. The solid, polyphase composition of matter of claim 7 whereinproeutectic crystals are scattered throughout the microstructure.

14. The solid, polyphase composition of matter according to claim 1,comprising in addition to the inorganic compound a member selected fromthe group consisting of Water, an element selected from the groupconsisting of Group 1A, 1B, 2A, 2B, 3A, 3B, 4A, 4B, 5A, 6A, 6B and 8elements of the Periodic Table of Elements, and mixtures thereof.

15. In the method of forming a solid, anisotropic polyphase compositionof matter having a microstructure of eutectic composition consistingsubstantially of three-dimensional crystallites of one phase of theeutectic'imbedded in another phase, including the steps of establishinga eutectic mixture, heating the mixture to a temperature above theeutectic temperature to melt a portion thereof throughout its entirecross-sectional area and to establish a liquid-solid interface,unidirectionally solidifying at the liquid-solid interface by moving theinterface in a direction such as to give the desired lamellarorientation, subjecting the interface to a cooling medium while theinterface is moving in said direction to thereby simultaneously solidifyat the interface at least two separate eutectic phases, and causing atleast one of the eutectic phases to grow in the form of threedimensionalcrystallites which are normal to the liquidsolid interface and parallelto the growth direction by regulating the solidification rate and thethermal gradient of the liquid at the liquid-solid interface so that theratio of the thermal gradient in the liquid phase at the solid-liquidinterface to the solidification rate is between about 0.1 and 1000C./cm. /hr., the improvement which comprises utilizing as the startingmaterial a eutectic mixture which is a member selected from the group ofeutectics consisting of: KCl-LiCl; BaFe O BaFe O MgCl -KCl; Al O TiOPbO-WO PbOPbM O FeO-FeS; CoO-FeS; Li CO CaCO Ca 2-NQNO3 the compositionof which eutectic mixture is such that the components thereof arereciprocally soluble in the liquid state, but simultaneously freeze outat a constant temperature into at least two different types of crystalsupon cooling from the liquid state.

16. The improvement of claim 15, wherein the eutectic mixture comprisesin addition to the inorganic compound a member selected from the groupconsisting of water and an element selected from the group consisting ofGroup 1A, 1B, 2A, 2B, 3A, 3B, 4A, 4B, 5A, 6A, 6B and 8 elements of thePeriodic Table of Elements, and mixtures thereof.

No references cited.

LEON D. ROSDOL, Primary Examiner I. GLUCK, Assistant Examiner US. Cl.X.R. 23--295, 296

